The proposed research will provide a management model for longfin eels, and the data to support the model in Queensland. Supporting data for NSW will be supplied by a collaborative project in that state. The model will also be suitable for managing shortfin eels in Victoria, Tasmania, NSW and Queensland, given appropriate data. The research will also develop methodology for a fishery-independent sustainability indicator, which will similarly be useful for both longfin and shortfin eels.
Glass eel fishing and the aquaculture it supports are developing industries throughout southern and eastern Australia, and are potentially worth tens of millions of dollars. Prices for adult eels have also increased in recent years, encouraging the growth of this industry. However, adult stocks in Queensland and NSW appear to be declining. In addition, eels comprise a major part of stream biomass, and are probably the most important predators in many freshwater ecosystems. Significant changes to stream ecology by major reductions in eel biomass have the potential to destabilise ecosystems, facilitating invasion by exotics among other problems.
The FRDC is supporting glass eel industry development. However, sustainability of glass and adult eel fishing is not yet being addressed. Internationally, eel fisheries have not been sustained. Glass eel supplies have collapsed in Europe, Asia, and North America.
Our modelling of Queensland eel stocks demonstrates two things. Firstly, fishing of adult eels can severely reduce the number of spawning females. This is backed up by evidence from New Zealand, where the Lake Ellesmere eel fishery has seen drastic declines in the number of (particularly female) spawners (Jellyman 1995). Thus some types of adult eel fishing may damage the glass eel fishery. On the other hand, reduced or redirected adult eel fishing may significantly enhance the glass eel fishery. A management model will provide insight into these issues. Modelling of the kind proposed has not previously been published for eels, and interest has been expressed by international eel researchers.
Secondly, very little is known about longfin eel demography and population structure, knowledge which is needed for informed management of eel stocks. Some very sparse demographic data come from New Zealand, Tasmania and Victoria, but even this is compromised by eels’ great variability in growth and maturation rates between environments. Queensland may hold the majority of longfin eel biomass in Australia, but no studies have been carried out either here or in NSW. Statistically sound fishery-independent techniques are required to estimate population structure and demography for all important sectors of the population, particularly females. Fishery-dependent techniques will not work in Queensland due to the decline of the fishery. Data from NSW will provide complementary information on males, which are probably seldom found outside estuaries.
As the glass eel fishery develops and as demand for adult eels rises, information on the changing status of wild eel stocks will be required. A sustainability indicator can provide this. Such indicators are best developed as early as possible in the evolution of the fishery.
Eel life histories are complex and unique, and successful management requires a different approach from other fisheries. Successful management of glass and adult eel fisheries requires a management model supported by demographic and fishery-based data. It also requires a feedback mechanism in the form of a sustainability indicator. The proposed research will provide the first and develop methodology for the second.
